1. Field of the Invention
The present invention relates to an apparatus for automatically detecting the size of a phonograph record placed on the turn table of a phonograph record player.
2. Description of the Prior Art
The phonograph record player for reproducing information from records handles records of a variety of sizes. The records (disc-like records) generally used at present are of three types by size, including 17 cm, 25 cm and 30 cm in diameter. In the automatic player wherein the pickup arm is automatically swung and the stylus of the pickup cartridge is placed down into the groove of the disc record disposed on the turn table, it is required that the size of the record placed on the turn table be detected thereby to determine the pickup stop position to which the arm swings as it moves toward the edge of the record disc. In other words, the stylus of the pickup cartridge is required to be set down properly onto the edge of the record.
In conventional phonograph record players, the size of the disc record to be reproduced, i.e., the stop position of the pickup arm is mechanically designated, so that the pickup arm swings to the designated position where it stops and then descends onto the record. This function is accomplished by a device for designating the size of the record, which device has a lever extending therefrom for determining the swing range of the pickup arm.
In such conventional apparatuses, the record size is required to be transmitted to the disc record player each time the size of the disc record changes, thus complicating the operation of the disc record player.